The ability of anticancer drugs to facilitate the acquisition of antitumor immunity by tumor bearers has been recognized. Several anticancer drugs such as cyclophosphamide (1-7), L-PAM4 (8), 1,3-bis(2-chloroethyl)-1-nitrosourea (9), vinblastine (10), fludarabine and bleomycin (11) have been shown to enhance the acquisition of T cell-mediated antitumor responses in a variety of animal tumor models (1, 5, 6, 8-11) and in patients with advanced melanoma (2-4) or advanced renal carcinoma (7).
Studies into the mechanisms through which the anticancer drugs enhance the acquisition of T cell-dependent tumor-eradicating immunity in tumor bearers revealed that the chemotherapy leads to a shift in the cytokine profile from anti-inflammatory cytokines (such as TGF-β and IL-10) with inhibitory activity for CTL generation toward proinflammatory cytokines (e.g., TNF-α, IFN-7, and GM-CSF) that favor the development of antitumor cell-mediated immunity.
In particular, fludarabine is an immunosuppressive purine analogue that has been used mostly in the treatment of indolent lymphoid malignancies (12). Repeated cycles of fludarabine therapy induce a profound T-cell depletion, particularly of CD4+ T cells (13). Unlike other immunosuppressive cytotoxic drugs, such as cyclophosphamide, fludarabine induces lymphocyte apoptosis in both dividing cells as well as cells in the G0-G1 phase of the cell cycle. This cell cycle independent activity may be attributed to the drug's inhibition of STAT1 signaling (14).
So far immuno-therapy of cancer and chronic infectious diseases has had limited success. The inventors show in the present application that a combination of lympho-ablative drugs with recombinant proteinous vaccines show much more encouraging results.
As lympho-ablative drugs kill (apoptosis) or render lymphocytes inactive (anergic), they are expected to reduce the effectiveness of vaccines that deliver antigens to professional antigen presenting cells.
In particular, the adenylate cyclase (CyaA) of Bordetella pertussis has the capacity to deliver its catalytic domain into the cytosol of eukaryotic cells (15). Thus CD4+ and CD8+ T cell epitopes inserted into the catalytic site of CyaA are processed and presented by MHC class II and I molecules, respectively, at the surface of antigen-presenting cells (APC; (16)).
Furthermore, CyaA was shown to bind specifically to the αMβ2 integrin (CD11b/CD18; (17)), and therefore to target these T cell epitopes to the CD11b+dendritic cell subpopulation (18).
Immunization of mice with recombinant CyaAs bearing appropriate T cell epitopes led to the induction of strong CTL responses, full protection against a lethal viral challenge, and efficient prophylactic and therapeutic anti-tumor immunity (19-21).
Despite many encouraging results at the pre-clinical level, translation of adoptive cell-based immunotherapies to the clinic has faced many failures. According to Rosenberg (22), the objective response rate of immunotherapeutic trials in cancer remains below 3%, the better results being obtained with techniques based on autologous adoptive cell transfer therapies. This approach is laborious, expensive and difficult to generalize safely. Hence, it is of interest to specify at the pre-clinical level, strategies to improve adoptive cell-based immunotherapies.